A transmitter output stage can emit the power generated thereby to an antenna resonant circuit coupled loosely thereto in optimum manner only if the resonant frequency of the antenna resonant circuit is exactly matched to the output frequency of the transmitter output stage. A mistuning of the antenna resonant circuit necessarily leads to a reduction of the radiated power and thus to a reduction of the achievable range of the transmitter. In particular with portable transmitter devices, which are operated under a great variety of ambient conditions, such mistuning or off-resonance of the antenna resonant circuit can occur. If for example relatively large iron components are located in the vicinity of the antenna resonant circuit this acts like a change of the inductance of the antenna resonant circuit and this in turn necessarily results in a change in the resonant frequency. The invention is based on the problem of providing a circuit arrangement of the type mentioned at the beginning in which irrespective of changing ambient influences, an optimum transmission of the output power of the transmitter output stage to the antenna resonant circuit is always achieved.